Coating metal



Patented Aug. 16, 1938 v COATING METAL- Leo P. Curtin, Cranbury, N. J.,minor to Cartin-Howc Corporation, poratlon of Delaware New York, N. Y.,a cor- No Drawing. Application January 2, 1,936, Serial No. 57,314

13 Claims. 01. 91-68) This invention relates to coating meta1;-and itcomprises a method of providing ferrous metal (iron and steel) oranother oxidizable metal with a protective coating wherein the metal isdipped 5 in or wet with an alkaline aqueous solution containing bariumand a permanganate; and it also comprises metal carrying a closelyadherent protective dark colored film of oxid nature and containingbarium, iron and manganese in various states of oxidation; all as morefully hereinafter set forth and as claimed.

I have found that by dipping or otherwise wetting iron and steel in anaqueous bath containing barium hydroxid and a permanganate, the

metal is quickly covered with a dark colored protective coating layeruseful in many relations. A solution containing 2 per cent bariumhydroxid (as the octahydrate) and 1.5 per cent commercial permanganateis satisfactory. Formation of the coating is accomplished in a minute orless.

While work at the ordinary temperature is practicable, it is more rapidand generally satisfactory to operate in the temperature range between60 and 100 C. The concentration of the components in the coating bath isnot at all critical; the potassium permanganate concentration may varyfrom 0.25 per cent to 3 per cent and that of the barium hydroxidoctahydrate from 0.5 per cent to 5 per cent. Below these limits, theaction of the solution is rather sluggish, while with solutions abovethe given limit, action is quite violent and adherence of the coating isnot satisfactory. The film formed is always dark, being dark green incolor when present in very thin layers and green to purple in color whensomewhat thicker. The film is not injured and is indeed improved in somerespects by heating. On heating for a minute or two at a temperaturesomewhat below red heat, the color of the coating is 40 changed to adull black.

While the stated solution made with potassium permanganate andcrystallized barium hydrate is satisfactory, other ways of making thebath may be used. A solution of barium hydroxid and 5 bariumpermanganate is particularly satisfactory. Barium permanganate has theadvantage of easy manufacture. Good results are obtained with a bathmade up with sodium hydroxid, barium nitrate and potassium permanganate.

It is a well known fact that permanganate ion is rendered somewhatunstable by the addition of alkali, and long boiling of a concentratedsolution of potassium permanganate and caustic potash results in someloss of oxygen and some formation of potassium manganate and alsomanganese dioxid. Such solutions have, however. but slight tendency tocoat iron and steel. Likewise, if a solution of potassium permanganatecontaining either strontium hydroxid or calcium hydroxid, butcontainingno barium ion, be heated to boiling and a sheet of clean ironintroduced, the tendency to coat iron is but little greater than if thesolution were made up exclusively of alkali metal compounds. 11', tosuch a solution, a small amount of any soluble barium salt be add- 10ed, such as barium nitrate or barium acetate, then the coating of themetal proceeds rapidly. Apparently, this tendency to coat iron and steelrises to a sharp maximum in the presence of hydroxyl ion, permanganateion and barium ion; if one of these three components be absent, thecoating tendency is but slight or entirely absent. A solution in whichthe barium is replaced by lead basic acetate shows some tendency to coatiron but is quite inferior to the bath containing bari- 20 um. It is notadvantageous vto use ammonia or an ammonium salt in such a bath becausea violent action is set up between the ammonia and the permanganate,resulting in the oxidation of the ammonia to gaseous nitrogen,principally, and the reduction of the permanganate to manganese dioxid.This reaction proceeds regardless of the presence or absence of metal.

The coating reaction takes place at the ordinary temperature but worksmore rapidly and 30 more satisfactorily at temperatures ranging betweenC. and C. It is believed that a reaction takes place between the iron orother metal and the permanganate which has been rendered unstable by thepresence of barium ion and hydroxyl ion, resulting in the oxidation 01the iron and the reduction of permanganates to manganates and tomaganese dioxid. The property 'of coating metal under the conditions ofthe baths above described is peculiar to permanganate ion; it is not aproperty of manganate ion, since it was found that a solution of sodiummanganate showed no tendency to coat iron either with a small amount offree caustic present or with a considerable amount of caustic alkali inthe bath.

The coating is believed to consist of a mixture of insoluble manganates,manganites and metallic oxids of iron, barium and manganese, alone or incombination.

As stated above, it is possible to have other ions present in the bathin addition to the three whose presence is essential. For example, theaddition of a soluble nitrate, such as barium nitrate or sodium nitrate,to the bath seems to re- 55 sult in a thinner but smoother and moreuniform coating. Other substances which are compatible with theessential elements of the bath may be In a practical embodiment of thepresent proc-.

ess, clean ferrous metal is dipped into a bath containing two per centof barium hydroxid octahyrlrate and 1.5 per cent potassium permanganate.The metal is held in the bath for one minuteat a temperature of 90 C. itis then withdrawn, washed and dried. If the heat treatment is to beapplied, it is heated at a temperature of 500 CI for 5 minutes. Anaddition to the bathof 3 per cent of sodium nitrate is beneficial insome cases. Other oxidizing agents having an effect similar to that ofsodium nitrate may replace sodium nitrate.

As stated, the coating produced as described is useful in a number ofways. It may be oiled with linseed oil or another oil, such as Perillaoil, soya. bean oil, etc., and the oil allowed to dry", .which it doeswith great rapidity. Manganese compounds are good drying agents and inthis case, the proportion is large. And manganese compounds furnishoxygen; so that air drying is not essential; If a paint, lacquer orvarnish containing a drying oil is applied over the coating and is thensubjected to baking at an elevated temperature, the manganese compoundsin the coating accelerate the hardening of the paint or varnish. Themanganated coating forms an excellent substratum for oil varnishes,lacquers, enamels, etc. The coated metal may be redipped in one of theordinary phosphate coating baths, giving a coating which is differentfrom the ordinary phosphate coatings and is in many respects superior.The phosphated film is then a better rustproofing agent. For many uses,the manganated film may be simply oiled with a non-volatile wax or aheavy oil, or it may be treated with a bituminous or asphalticcomposition, advantageously diluted or thinned with a volatile solvent.In some cases,

the liquid may carry an oil soluble dye. An important new utility ispreparing iron and steel for the application of vitreous enamels,compositions which are fused on the metal at a fairly high temperature.As is well known, it is difficult to prepare clean iron and steel sothat a good bond is effected with this class of enamels. Sometimes, themetal is sand blasted, which is a good expedient but rather expensive.

The main utility of the new manganated film is, however, as a substratumfor paints and lacquers. For this purpose, it may or may not be oiled orphosphated.

As stated, the coating bath may include nitrates. These are found toexercise an advantageous action in the coating process.

Non-ferrous oxidizable metals may be given a manganated coating in theway described for iron and steel; the procedure and the final re-.

suit being the same, save that iron is not now a component .of the dim,an oxld of the other metal (copper, tin, zinc, brass, lead, etc.) takingits place.

What I claim is:

1. The process of producing a protective coating on an oxidizable metalof a class consisting of iron and steel, zinc, brass, copper, tin andlead which comprises treating the surface of the metal with a solutioncomprising a soluble permanganate, a soluble barium compound and asoluble hydroxid, washing the resulting coating free from mother liquorand drying it.

2. The process of producing a protective coating on an oxidizable metalof a class consisting of iron and steel, zinc, brass, copper, tin andlead which comprises treating the surface of the metal with a solutioncontaining a soluble permanganate, a soluble barium salt, a solublemetal hydroxid and an oxidizing agent other than permanganate.

3. The process of claim 1 wherein the metal to be treated is ferrousmetal.

4. The process of claim 2 wherein the second oxidizing agent is asoluble nitrate.

5. The process of claim 1 wherein the permanganate ion is present as analkali metal permanganate.

6. The process of claim 1 wherein the soluble barium compound is bariumhydroxid.

7. A solution for the production of protective coatings on oxidizablemetals which comprises permanganate ion, barium ion and hydroxyl ion.

8. A solution for the production of protective coatings on oxidizablemetal containing barium permanganate and barium hydroxid.

9. As a new material, an oxidizable metal of a class consisting of ironand steel, zinc, brass, copper, tin and lead bearing a coating producedby the action on the metal of a solution comprising permanganate iron,barium ion and hydroxyl ion.

10. Ferrous metal carrying a surface coating produced by the action uponthe metal of a solution comprising permanganate iron, barium ion andhydroxyl ion.

11. Ferrous metal carrying a dark protective coating of oxid nature,containing iron, barium and manganese, and formed by action upon themetal of an alkaline solution containing barium permanganate, themanganese in the coating being in various stages of oxidation lower thanthe permanganate stage.

12. Ferrous metal carrying an adherent manganated coating formed uponthe metal by a coating solution comprising permanganate ion, barium ionand hydroxyl ion and a finish coat of oil, paint, varnish lacquer orenamel bound to the metal by said manganate coating.

13. Ferrous metal carrying an adherent manganated coating formed uponthe metal by a coating solution containing barium permangamate andbarium hydroxid and a finish coat containing a drying oil baked upon andhardened by said manganate coating.

LEO P. CURTIN.

